Differential refractometer



Oct. 7, 1952 ss 2,612,814

DIFFERENTIAL REFRACTOMETER 5 Sheets-Sheet 1 Filed May 26, 1948 E0 6.614488% BY AT TORNE' Y Oct. 7, 1952 L, G, GLASSER 2,612,814

DIFFERENTIAL REFRACTOMETER Filed May 26, 1948 5 Sheets-Sheet 2 v I INVENTOIC M0 6. GLASSE'R ATI'0RNE Y Oct. 7, 1952 L. G. GLASSER DIFFERENTIAL REFRACTOMETER 5 Sheets-Sheet 3 Filed May 26. 1948 IIII L INVENTOR. LEO q. (iLAssE'R ATTORNEY Oct. 7, 1952 1.. G. GLASSER 2,612,814

DIFFERENTIAL REFRACTOMETER Filed May 26, 1948 5 Sheets-Sheet 4 IN VEN TOR. LEO 6. GLASSER Oct. 7, 1952 G. GLASSER 2,612,814

DIFFERENTIAL REFRACTOMETER Filed May 26. 1948 5 Sheets-Sheet 5 I ss\ 5 87-" Lass IN VEN TOR. LEO 6. GLASSE'R ATTORA/Z'Y Patented Oct. 7, 1952 I 2,612,814 DIFFERENTIAL REFRACTOMETEB Leo G. Glasser, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware 7 Application May 26, 1948, Serial No. 29,279

This invention relates to differential refractometers and particularly to those devices for the determination of differential refractive index values wherein the precise location of the refracted light beam is determined by electricaloptical means.

It is well known that a beam of light is refracted, or deflected, away from its course, when it passes obliquely from one medium into another medium and this characteristic, depending as it does upon the specific nature of any light transmitting substance, has been utilized as a means of quantitative analysis. The index of refraction (n) of a particular substance is a measure of the extent to which an oblique light beam is 'deflected in its passage through the substance and, when the light enters the substance from the air, is defined as the ratio of the sine int to the sine Tm, where i is the angle of incidence of the light beam as measured from the normal to the surface of the substance and Tm is the angle of refraction for the substance, which is the angle between the nor-mal and the line of the new path taken by the light beam after it has entered the substance.

The value of the refractive index 'of a substance varies with temperature, a temperature rise in the case of some organic liquids causing a decrease in n to the extent of about 5.5 10- for an increase of 1 C. at temperatures considerably below the boiling points and an even wider variation at higher temperature levels. It is therefore desirable to control the temperature of the sample material rather closely to insure accurate measurements.

The value of the refractive index of a substance is also dependent upon the wave length of the light which is used in the measurement, n for benzene, for example, being 1.49759 when measured with red light of a wavelength of 6563 A. at 29 (2., and 1.52487 when measured With violet light of a wave length of 4341 A. at the same temperature.

The index of refraction characteristic is particularly useful as a means for the determination of the concentration of a specific solute in a solvent, In some cases widely different concentrations of a particular solute in a' particular solvent may have identical refractive index characteristics; but if this fact is established by prelim- 10 Claims. (Cl. 88-14) inary investigation of the particular solute-sol vent system, it is possible to utilize refractive index techniques to measure concentrations over all ranges where no such overlapping occurs; In

these" analyses a plot of refractive index versus known standard concentrations of the particular material dissolved in the specific solvent employed may be drawn, and any concentration of the same material in the same solvent maybe" thereafter determined'by simply measuring the refractive index and then referring to the concentration-refractive index curve to determine the exact concentration which corresponds'to the observed value of refractive index.

. The accuracy with which the refractive index characteristic can be determined depends, of

course, upon the accuracy of themeasurement of.

the light beam deviatloninztraversing the medium tested. A high degree of precision in such measurement has been attained in the manual laboratory type refractometer by the use of very accurate scales and associated'equipment; however, the visual determination of refractive-indexvalues is a relatively slow and tedious operation,

' and moreoverfis dependent, in part at least, upon personnel are available to prepare the samples, perform the measurements and record the ob served results. i y

In a great variety of liquid phase chemical manufacturing operations very effective process control may be attained if process material compositions can be continuously-evaluated and regulated within preselected limits. The continuous determination of the differential value between the refractive index of the process material and the refractiveindex of a standard reference material, hereinafter abbreviated An, affords a convenient method for achieving such process control.

A primary object of this invention is to provide a simple, reliable differential refractometer.

Another object of this invention is to provide a differential refractometer employing electricaloptical means for the measurementof light de flection. n

Another object of this invention is toprovide a differential refractometer capable of continuous measurement of refractive index values;

Another object of this invention is to provide a differential refractometer which automatically determines andrecords refractive index values. 7 Another object of this invention is to provide a differential refractometer wherein enviroment Figure 1 is a diagrammatic representation.of.

the general arrangement of the optical elements and phototubes according to this invention.

Figure 2 is a diagrammaticrepresentation of the electrical circuit which is employed in corrjunction with the optical system1ptFigure- 1. Figure 3 is a perspective view of onet pe of holder used for the support of a light fi1teror light slit plate.

Figure 4 is afront view-o1one= type; ofglightslit plate-which maybe. used. with this. invention.

' Figure- 5' is a sectional view: of .a lens: retaining- 1' holder-t" Figure 6 is a sectional. view. of: a-.lens.:ring.-

Figure! is bracket.

'Figure- 8 is a front view .of'the lens supporting" bracket shown in plan in Figurefl.

Figure 9 1s a perspective view of-:one: type of sample cell, showing. the arrangementof connectio'ns 'i'or theisupply andremoval of.;the, same ple andstandardliquids.

Figure ld'i'szaitopzplan views oi the sample; cell.

or 'Figurer 9 with the cover: plate removed.-

Figure :11 is an; end view Qf-the -.sam le.;cell of Figure .:with" both" theendiand .top. co.ver.:plates removed:

Figure-1211s a frontxelevationuview, of: a. cell. or.

prism window retaining-ring.

I lgure213ii's a isectionalxview-taken. along line:

Figure: 1461s a. side elevatinnvview in. partial.

section ofJa rotatable .glasszplate holder;

'Ffig'u're'ilfi. is. a top; plan...view.;of;-,a chamber. housing thesdividingsmlrrorztheuli ht measuring; phototubesa andythe electrometer; tuba with the. topicover platezremnyedi.thelight;shutterelement. and allf electrical.- conneotiqnsj being ornitted.:for

clarity in representation.

"fi ures 16.,is ja partial sectiontaken. .along line I 6;'l 6.0!; Figure; 15:.

Figure .1.7..is::a; rearelevatiorrview.of. the cham; ber;shownjinrlifi ure.15 .with. both, top, and, back rrplates; emoved. nd. the; li ht shutter e1e.- menhassembledi the: electrical connections being. omitted.

Figure-1.81s a perfi fi tive. view of oneetyperof diiiusing plate holden.

Flgi 1r,e 19. is a; front elevationview; of one. type of light regulating shutter.

' Figure :is a side ,elevation.view. ofthe shutter shown Figure-19.

' Figure 21 is a; side; eelvation; view. ofone; assembly; of ap fllatus which; can be. utilized to measure" diiierential,,refractive. index. .values according to this invention.

The. objects of, this invention are rattain ectby providing, a device. whichh is adapted, to. .continuously determinethegdifierential bet ween the refractive index of the sample material and .the refractive index; of a standard reference ma.-

terial, and either givean-indication of the-.difierrential .valueor. record the; extentof, this difiera top-planview of a lensrsupportingtrical-responses between the point of zero differentialan'd'the existing state is indicated and recorded The null-balancing instrument is preferred for'plant use because of its high inherent operating stability over relatively long periods, however, the off-balance! measuring embodiment possesses :much. higher; sensitivity; and thusmay be; advantageously utilized; in. laboratoriesv or; other; locations, where occasional-check; calibra-.-

tions are notobjectipnable; Even the latter'dis.

advanta e may-b t. atsely, over om y= nl y- A ing an electrometer tube of a type wherein: volt age. changes on therid; tn l b n alter: the. operating characteristics. of the tube over the measuring.- range involved.

The samegeneral Y optical system; may be r uti.- lized;.for both. the nullsbalancinga-and :off -.ba1ance-. measuring embodiments off this invention, and. the; optical principles. of operation of. both -em.-- bodimen-ts. will: be: described; with reference, to; Figure 1? Thelight sourceflndicated ;a t l emits the-Jightwhich. is, made; to; traverse? the optical; path. through; the light. transparent! sample cell. and: givaan. indication. ot-the di-fierence in' refractive index between; the sample. material, and the r standard material. monochromaticlight. source; suchg asg agsodiun arcrmay be. employed; inwhich'case no rllight filter such. as the filter-2 6-. herelnaiter; described,- need'.-be;-usedwto-. control, the quality of the light. If measurementssoifdifferential reiractlve'rindex are i to. be 1 made. over a rela vely; i e. a'nses. f exam l r. n .1,- a. required: accuracy. 0t: only; about .0-.00.1,- lightfilters may; be -dispensed with; if; an ordinary; tungsten; filament incandescent. lamp is.

usedasthelight-source; Ordinarily; however; it is preferred to usea. mediumz pressure: mercury vapor lamp; together-with. a. suitable .light filter fort-the, reason-that no. means for. light intensity regulation is then required and,. furthermore, the average intensityof-the light: emitted isrelatively constant over long. periods, of time.

Lig ht filter 6: may be azconventional narrow bandspass;type, or atfilter passing afairly wide band; of light -may be employed. if, an increased light intensity isdesireds The -purpose of.filter 6. is to,control the supply of light to within. a more or less constant range of wave-lengths, so that light of substantially the. same color; wilLbe reflected' -to each ofthe measuring phototubes hereinafterdescrihed, and thereby insure that the indication of.the phototubes will be substantially independent of variations in light. source quality. Filterfi is preferably interposed inthe light path ahead a of, sample .cell. 1. so, that the liltterwilleliminate light :which. might heatup. the sampleor standard, era-decompose the, compo: nents...

The lens arrangement. shown. in Figure ..1 is preferred,- but it.;wi1l be .understoodthat .thisan system.

rangement is susceptible of wide variations and in some cases some of the lenses may be dispensed with. As shown,-the light emitted from source I is first preferably passed through condensing lens 2 which focuses the light on slit 3. Here the light is constricted to a moderately broad line after which it passes to collimating lens 4 which is preferably masked by diaphragm 5 toprevent undesired light leakage around the edges of this lens. The parallel beam of light next traverses filter .6 which permits the passage of light within the desired range of wavelengths and screens out the balance of the light. The parallel light beam emerging from filter 6 then passes into the sample cell I, the entering window of which is disposed perpendicular to the direction of light travel so that the light beam will not be deflected from its course upon'entering the sample material within the cell.

While both lenses 2 and 4 may be dispensed with, it is advantageous to employ them for the I reason that they concentratethe light to a higher intensity and at the same time reduce stray light effects. If this desirable light control is not required, lens 2 can be eliminated without necessitating any changes in the other lenses of the If lens 4 is eliminated, lens 9 located after sample cell i must be chosen so that its focal length is such that it will still focus an image of slit 3 on the faces of the dividing mirror hereinafter described. At least one focusing lens, either 9 or 4, must be employed to form the image of slit 3, but either of these lenses may be eliminated if the focal length of the other is such that the image will still be formed at or near the plane defined by the dividing edge of the mirror and the axes of the phototubes.

Sample cell 1 encloses the sample material and the standard material, the differential refractive index value of which is to be determined. The

standard material is preferably interposed as a light transparent prism 8 across the light path, while the liquid samplematerial is continuously circulated through the 'cell and aro-und'prism 8; it will be understood, however, that the positions of the two materials may be reversed so that the sample occupies the space inside the prism while the standard is circulated around the outside when desired. The vertex of prism 8 is disposed along a line parallel to light slit 3 with the walls of the prism oblique to the measuring light beam. It will be understood that prism 8 may be fabricated from any solid transparent material such as glass, properly oriented quartz, or a polymeric substance that has a refractive index such that it will serve as a standard of comparison for the sample-material. Thus, if it is desired to maintain the sample material at a preselected composition which has a characteristic value of refractive index, prism 8 may be fabricated as a single piece from a material having the same characteristic refractive index. However, it is preferred to employ a hollow prism 8 which may be filled with a standard solution of any preselected value of refractive index, for the reason 7 that a suitable standard is thereby more readily position, or, in any case, when the sample mate'-' rial and the standard material'have the sameornearly the same refractive index and rate of change 'of refractive index with temperature,

spurious refractions due to ambient temperature changes will be negligible forsmall values of An.

To insure equality of the temperature of the sample material and'the standard material it is preferred to house the entire assembly of analytical equipment within a light proof heavily insulated cabinet which is fitted with a suitable thermostat for close temperature control. The liquid sample material may be first brought to approximately the desired temperature level by circulation through an external temperature controller, and then to final temperature by passage through a heat transfer unit of sufiiciently large heat capacity, such as a relatively long pipe coil;

which is mounted within the equipment cabinet. It will be understood that under these conditions the sample cell temperature may be maintained at any desired level either above or below the level of the process temperatures maintained in themanufacturing system. Since the construction of the temperature regulation system is only indirectly related to this invention it has not been further described herein. In the preferred case the. light beam entering cell 1 traverses first the sample material and then the standard material; since the light enters thecell on a normal line, however, it will not be deflected from its courseby the sample materials If the refractive index of the" standard material of prism 8 is the same as that of the sample it will be apparent that the light beam will not be measurably deflected in transit through the prism and will emerge from the exit window of cell i alon the same course at which it entered. If the refractive index of the sample material surround ing prism 8 is different from that of the standard material within the prism, the light beam will be deflected either up or down in the plane" of Figure 1 an amount which is proportional and is brought to a focus at or near the plane de fined by the sharp edge of dividing mirror land the axes of the two phototubes.

Both the null-balancing and the off-balance measuring embodiments of this invention employ a dividing mirror It! to effect a division of the measuring light beam so that's, portion of the incident light is reflected to each. of the phototubes IZ and I3. Dividing mirror It] comprises a body portion having two faces inclined at equal angles on opposite sides of the dividing edge, which is disposed toward the light source. Small mirrors Illa and lllb are mounted on each of the faces so that light incident thereon is reflected to the phototubes. Phototubes i2 and I3 are conventional devices the internal resistance of which varies with the illumination received. so that the tubes pass small electrical currents which are proportional to the inoident-lightrefiected to them. I The optical elements described in the foregothis device irmrawiofqrpzeciselmthe-:sameaconstructionPin;

null-ibaiancing:andiofibalancesmeasure in; embodiments; of thlszinventionz however a I difierentcmieronmounting may-:beemployed for eachstofstherembndiments, and thezdeta'ils of .t-hBSGzmountinzsiwillhewbe.:described.-.

In the nullsbalancingtembodimentthesupport+ ins Jame-oi :dividingrmirror: l is threaded to. relceivexmicrometertzscrew IL: upon. which: it'pis' mountedzlin none-rotatable .relation'shipaso that which ,is'. reflected'stoseachxot the: phototubes: by mdvingrmirrorreln by: rotating :screw 1 lsuitablyinteither aaclookwiseaor:counter clockwise direc.

tion; Thez exacti amount ofgdeflection: ofthe. ligh-t' beam sat thez'pointwofzlightzbalance. can. be: conveniently :-determinedlbyiproviding: a: calibrated dlVlflediclrClE: integral; with l'screw-t H and: a fixed;

index i lir'ie 1.0m arr-:sadjacent: surface,v whereupon 1 the"movementiot.thedividing'mirrortto,either'side tained 'byfdirect reading, if desired: v As: willtbe hereinatter describedfi: this :balancing 'aoperation isfpreferably eifectedrhy: suitable automatic auxiliary devices which, at the:same.-:time, either give an: indication "or: recording: 'ofthe amount 'of :the

deflection,:oriactuatesuitable control mechanisms: toxalter rtheicomposition- 0f?thersample: material see that the deflection-is; restored "to: substantially zeroz" IlT-Willijbfi' apparent that agreatly increased rangeot:deflectionimeasurement may be; attained by utilizingfazmovablerdividing mirror of thenature employed'zim this embodiment; since deflectionsiibeyonduthez:bounds.10f: the: mirror faces maybe; reflectethbyymerely shiftingythe dividing. mirrori-to'a ,new positiont where the light beam willimpingeiupon -these-faces As: distinguished from: the. null-balancing em- A bodiment; the off-balance measuring embodiment ofizthisl-inventionwmay employ-a dividing mirror I it 'which. is fixedlyv mounted; at the approximate point .where-theecenter. ofan undeflected light:

pointlofithebeamlby directmeasurement. How-- i ever, ther flnalnreflned adjustment to the condi-' tion where equalyamountsl oi. light. are. reflected.

tolbothfcf the! phototubes ispreferably made byretracting ..the..light a.suitable degree. in compensationubyishiiting it by the movement of glass plate l4 hereinafter, described, or mounting thetdividing mirror on acalib'rat'ed micrometer screwtidenticalLwith screw ll hereinbefore described, and then adjusting the mirror's position'to the exactpointcorresponding t zero' net deflection. Once theyinitial" correction. de-' scribed has been-made ittwillgbe understood that thepositionof'the' element'used to eflect this compensation is not' thereafter altered until a new" 'zem-point setting is required: The instrument can-be-initially"calibrated' bypassing a series of solutions-having' 'known compositions around-*-prism S' 'and measuring the degree of electrical oiT-balance'which occurs in the circuit including: phototubes 1 land l3 by employing conventional 'devicessuch: as an indicating or recording voltmeter, for example. Y A plot of electricaizzofi-balance' versus compositions will then make it possible to determine the: composition oti'xany'. unknown-samples: which fall a. withim the .10 rotation: of screw l- -movesf .mirrortlflf either UPI: onfdown-in the planeofFigurel'. I Thissmounting makesritfpossibl'e toi baiancetheramountcf light:

8:17; diflerential: refractive index: encompassed.- by-thecalibrations In both? thee null-balancing and ctr-balance: measuringembodiments; thedividing edge 10!: mirror 10. may be disposed-inf the same-plane :ora paralleli plane to. that [of the; slit image focused:- by'iensw-S; or. may be: slightly inclined-tethe: vertical; axis of" the imagewby; a. small rotation. in a plane: perpendicular to. the light beamso': that; as changeslirr. the difl'erential' refractive index valuei'occur, the-i length-o1 the slitimage. reflected. to. the phototubes varies: This incline-s tion' is particularly advantageous @in the; oflbal-i ance measuring embodimentv where the: position of the: dividing mirror? is fixed, because :the: light: image; issdivided-between the -.-two mirror faces over= axsomewhat: greater: range? of deflectionsi than. would (be-the case if. the-dividing .edgel'were" exactly parallel to the slit: image;. particularLv-i where the: width of slit=3 .iSf relatively small; and the-trange; of-rmeasurement. is correspondinglyrincreased. The'amount ofv thisinclination isspret-l erablysmall a l /g -to 2 degree :rotation being employedfor a 1 light slit with. a width. of about; 0.1 mm: Since 'a-'slightinclinationofithex-dia viding mirror. edge tor-the. axis of the slit image; has; a positive advantage-under. the conditions: described it will be apparent" that in the null-- balancing embodimentit islnot necessary that? the-dividingmirror be: at all times maintained? exactlyperpendicular to thelight beamiso long: as'it is prevented: from cocking so that-unequal: amounts of light! are thereby reflected to the: phototubes.- Fromthe foregoing itiwill' also-be: understood: that preciserfocusing oftlens 9 is not: necessary to the'proper functioning. of the' device.

Glass plate lkinterposed between lens 9-and dividing mirror Ill, is a transparent plane -parallel glass-plate'rotatably mounted upon-a ver-' tical shaft-which is disposed 'out-of thetpath 'of thelight beam inprolongation: with a lineabi-b sectingthe undeflected light beam and parallel .to the plane of. slit 3. Plate- I 4 is preferably emplayed with each embodiment 01' this invention; It can, however, be made to serve a different purpose in each, and -may be: eliminated-rentirely if the functions it performs are not re'-- quired.

When plate l4--is. perpendicularly disposed across the light path it will not deflect thebeam', butif the plate is rota-ted'in. a clockwise direction the-light beam will be. deflected downwardly 1n=thev plane-of Figure 1 and, if the plate. is rotated in a counterclockwise direction x it will deflect thelight beamupwards. In the case of both. embodiments" plate." I l-ma'y-i beradvanta; geously employed to' train-the. measuring light beam-at-the precise zeropointof the dividing mirror for the position chosen' asuth' reference upon which subsequentdeterminationsof A nare' to be based; When this method of'zero point selection is-utilizedit will beapparentthat slight deviations of lightwhich'arise' from the passage or the light, through: the several cell and prism wmclowswill: be compensated" for without regard to their absolute magnitude: Using this method 1t is-likewise possibleatoiemploy a standardmaterial whichtl possesses a'refractive' index appreciably different from: the' value' at which it 1s desired tosmaintairrlthe' sample -material; correcting 'for the initial difference between standard and sample; andathus greatly simplifying the selectionazof 'a suitablefistandard material. The

described: method'for zero .pointlsemetion 9i tieularly important in the case of the oil-balancexmeasuring embodiment of this invention, because it does not necessitate changing the fixed mounting of the dividing mirror for a samplestandard system wherein the undeflected beam does not impinge exactly on the dividing edge of the mirror, the amount of this initial variance being compensated by deflecting the beam a suitable amount so that it will coincide with the dividing edge of the mirror. In the null-balancing embodiment the same initial zero point adjustment is desirable so that dividing mirror III will be disposed at the midlength of micrometer screw II, and the base line of the screws divided circle will be exactly opposite the fixed reference line. The null-balancing embodiment can, of course, be made to measure light deflections from some arbitrary base line corresponding to a different length of micrometer screw than the midlength, and the zero point setting obtained byvarying the position of the dividing mirror either up or down until the output of reflected light to each phototube is equal; however, the use of a relatively thin plate I4 of the order of about 2 mm. thickness affords a more accurate way of obtaining this initial setting and is preferably utilized in this case as well. It will be understood that when plate I4 is used to effect the zero point adjustment it will be turned to the point where it brings the undeflected light beam from cell 1 to bear on the dividing edge of mirror I0 after which its setting will not be altered until the evaluation of a new sampilestandard system makes it necessary to efiect a different initial compensation. The supporting shaft of plate I4 may be provided with a divided circle and a fixed index point in the same manner as has been described for micrometer screw II to permit the direct determination of the setting of plate I4.

In the null-balancing embodiment of this invention, glass plate I4 may be used for an entirely different purpose than that hereinbefore described. In this embodiment electrical balance is achieved at each light deflection by altering the light output to each of the two phototubes so that equal amounts of light are reflected to each tube. As will hereinafter be described in greater detail this light balance may be efiected by moving dividing mirror I I! to some new balance point by manipulation of micrometer screw I I. But, it

will be apparent that the same effect may be secured by maintaining dividing mirror ID in a fixed position and alterin the position of plate I I to new positions corresponding to balance at each of the varying light deflections. In this case it will be understood that plate I4 cannot at the same time be used for zero point adjustment but it is possible to vary the setting of dividing mirror I 0 to achieve this adjustment. When used to determine light deflections, plate I I may be advantageously fabricated of somewhat thicker glass than is utilized where the plate functions in a zero point adjustment capacity, since the degree of light deflection increases with thickness, and

the range of detection is thereby correspondingly increased. In this case it may be desirable to utilize a plate of a thickness of about 6 mm. or

even greater, but it will be understood that, as the phototube circuit in combination with an electrometer circuit. The purpose of thephototube circuit is of course to detect changes in light balance which result from varying light deflections and emit a characteristic electrical signal for each of the several deflections. The purpose of the electrometer circuit is to receive the electrical signals from the phototube circuit without at the same time causing any interference with the phototube circuits detection functioning. The same combination circuit is utilized with both the null-balancing and. off-balance measuring embodiments, the only difierence being that the output signal of the electrometer circuit is used to effect optical rebalance in the null- 1 balancing embodiment while, in the case of the off-balance measuring embodiment, the output signal is passed to a conventional voltage recording device.

The phototube circuitcomprises the two phototubes I2 and I3, the anode of one of which is connected to the cathode'of the other while the remaining tube elements are connected to the terminals of battery I5, the midpoint of which is groundedat I6. As shown, each half of battery I5 constitutes one arm of a bridge circuit while phototubes I2 and I3 constitute the remaining two arms. This bridge circuit may properly be termed or designated as a series-aiding light responsive electrical circuit. When .an equal amount of light is reflected to each of the phototubes the electrical potential at point I! of the phototube circuit will be zero, if the sensitivity of the phototubes is equal.

Point I1 is connected to grid I8 of one triode section of the double triode electrometer tube I9. The electrometer circuit comprises electrometer tube I9, battery 20, equal resistances 22 and 23 and output leads 24- and 25. The two cathode elements; of electrometer tube I9 are heated by resistance elements 46 in parallel connection which are supplied with .current from a. common outside source not shown.

As shown, both triode sections are supplied from a common voltage source 20 and both cathode elements are grounded at 26 through their respective resistors 22 and 23 so that the potential between points 28 and 29 will be zero, as long as the electrical potential of grid I8 remains at zero level. When one of. thephototubes, for example I2 of Figure 2, receives more light than phototube I3 due to the deviation of the measuring light beam, a more positive electrical potential relativeto ground is impressed upon both point I1 and grid I8, the grid current remainin almost zero in magnitude; i Under these conditions a large electron current passes between cathode 26 y and plate 21, and the potential of point 28 approaches that of plate 21; that is, it ishighly positive with respect to point 29; Conversely, when phototube I3 receives more light than phototube I2, the grid potential changes to negative and the flow of electron current decreases proportionately, whereupon the potential at point 28 approaches that of ground and becomes negative relative to its condition when responsive to phototube I2, at the same time becoming negative with respect to point 29. In this connection, the right-hand triode section always provides a reference for comparison with the left-hand triode section, any potential difference across leads 24 and 25 being, for all practical purposes, solely the result of changes in potential at point I! of the phototube circuit, regardless of the absolute potential level which may exist in'the electrometer circuit due to slight changes interminalvoltage of battery 20 upon prolonged use, or from other causes.

The double triode electrometer tube l9 performs its function of transforming the relatively weak input from the phototube circuit to an output at a higher powerlevel without interfering with the functioning of the phototube circuit. The double tri- -ode construction is especially preferred because all elements are housed in a common envelope where changes in gas pressure and ambient temperatures will affect each section alike and'thus prevent variations'in operation which might resultif theenvironments of the two triode sections'were different. However, it will be under- "stood thatother types ofelectrometer tubes may be utilized,-depending upon theparticular tube characteristics which are desired.

-As-hreinbefore-stated, the off-balance measuring embodiment of this invention utilizes a con- -ventional recording voltmeter (not shown) to indicate variations indifferential refractive index, the voltmeter being connected directly to leads 24 and 25.

The null-balancing embodiment necessitates theme of the additional conventional auxiliary equipment indicated generally at 39 in Figure 2 to restore the opticalbalance of the system upon each change in light deflection. Device 30 receives the direct current signal voltage from leads 24 and 25, converts this signal to'alternat- -ingcurrent of a phase relative to the alternating line current which is determined by' the polarity of the input current, amplifies the resultant current and supplies this current to one winding of the brushless, reversible, variable speed, two. phase induction motor 3|. The other .winding of motor 3I is continuously energized by ordinary 110 volt alternating current line voltage. Motor 31 responds to-thesignal current received from 30, rotating-in one direction upon the reception of electric currentof a phase correspondingto one polarity of signal from leads 24 and 25, and rotating in the oppositedirection .upon reception Of electric-currentofa different phase corresponding to 'theopposite polarity.

Optical balance at-each of theseverallight deflections corresponding to different values of differential refractive index'is restored by coupling the shaft ofmotor 3| tomicrom'eter screw it or. to the rotatable shaft of.plate 14, if it is desired to utilize the plate instead of the mirror to- -effect rebalancing. At the same time a recording of the amountof light deflection may be secured by mounting the movable center tap .of' a; conventional helical type resistance upon either micrometer screw 1 l or the rotatable shaft of plate I4, depending upon which device is .utilized to restore optical balance,.and connecting the two leads of this divided resistance in a circuit with a conventional automatic null-balancing recorder. With this arrangement the two divided portions of the helical resistance will function'as two arms of a bridge circuit, the other two arms of which areran integral part of the recording device circuit. One of "the resistance arms of the recorder isproVided With a movable tap, the position of which is continuously altered to correspond with-the position taken by thercenter tap of the-helical resistance, the bridge circuit of which these elements are part being continuously balanced by null-balancingelectrical means which are an integral part of the recorder mechanism. #The electricmotor whichrestores electrical balance in the bridge circuit described actuates the recorder. pen,; the

portions of holders 36.

position-of which varies in accordance =with1the position of the center .tap oflthehelical-lresistance,thereby tracing a recorder. both'theamount and the direction of light :deflection. 'Theiindication of the recordin device 'is interpreted in terms of refractive index by prior :empiricalcalibration using various liquid of known refractive index as standards.

The recording device utilized in conjunction with this invention-may be of. a conventional type which accomplishes. a control function. in addition to its recording-function,iunder wlii'ch conditions it may control the opening or closing of a regulating valve in aprocess-linetdintroduce more or less of one of the ichemicahcomponents to thereby restore the composition Lto an analysis'which is withinrthe preselected range of-diiferential refractiveindex values.

Thedetailed construction of the various elements of equipment utilized'withthe refractometer of thisinvention may be varied widely; but elements designed as hereinafter described have proved entirely suitable for the purposes contemplated.

As indicated in Figure 21-all equipmentmay be conveniently mounted on a common base member 32 which may be a metal I-beam section, the top surface of which is accuratelymachined so that allelem'ents are disposed in the Figures '7 and 8. These lenses may becf ordinary spectacle glass quality preferably supported within annular threaded holders. 36 (refer 'Fig..-.5) with'their forward faces contacting shoulders 31. The lenses are retained in position. byannular threaded rings .38 (refer Fig. .6) which are adapted to engage with the internal threaded Rings-38 are provided with two slots 39 oppositelydisposed to facilitate screwed assembly with holders 36. Suitableresilient gaskets may be interposed between the lenses and the metal surfaces of the holders and rings to cushion the lenses against breakage. Supporting frames '35 are tapped at points 40 to receive set screws which retain the lenses in a fixed position, and the base portion is provided with holes 4| for the reception of the screws which connect the framesto base memberfl.

Holders 42 (refer Figure 3) used to support slit plate 3 and filter 6, comprise a slotted plate receiving head portion, provided with a 'cut out window 43, which is supported by the standard 44, the foot of-which is provided at-45 with screw openings for attachment to base 'member'32. The slots on each side of the holder are closed off at the bottom to provide supporting-ledges upon which the lower edge of the slit plate or light fllter rest, and spring clips 41 retainthese elements in fixed position parallel to andagainst the wall containing window 43.

The particular slit plate 48 shown in Figure 4 comprises a thin plate of light impenetrable ma.- terial, such as metal, which isprovided with a ruled perpendicularly disposed light opening 59 which'may vary in width from about 0.1 mm. to as much as about 7.0 mm., or even greater, dependin upon the width of mirror faces Illa and [01). If relatively wide mirror faces are employed it will be apparent that a wide light slit may be utilized, so long as the entire expanse of mirror surface is not covered by the impinging light beam at any one time. It will be understood that it is advantageous to employ a relatively wide light slit, because slight dimensional variations caused by inaccuracies in machining, springing of the plate or obstruction by minute dust or lint particles will then only cause a very small percentage variation in light throughput, thereby preventing errors in determination aris ing from large inequalities in the light supplied to the mirror faces. Solid slit plates made from glass coated with vaporized metal at all points except the slit are especially suitablebecause they contain no aperture within which dust can accumulate. Also, the slit may be defined by two separate metal pieces, the true edges of which are arranged inopposition, such as by a pair of safety razor blades, if preferred.

Sample cell 1 shown in Figures 9, 10, and 11, comprises a. completely enclosed chamber which may be fabricated from a series of metal plates assembled together with screws 56. The; cell may be connected to base member as "with screws which are introduced from the inside of the chamber through counter-sunk holes drilled in the bottom plate. Cell 1 is provided with transparent glass light inlet and outlet windows 52 disposed at the level of the measuring light beam. It will be understood that sample cell 1 may be widely varied in design and may even conveniently constitute a section of process piping. As shown, the liquid sample material is introduced into cell '7 through pipe coupling 53 and is removed on the opposite side of the chamber through pipe coupling 54. I

A hollow standard prism 8 is illustrated in the drawings, it being understood that a solid prism of suitable material may be substituted if preferred. As shown, prism 8 is disposed in the path of the measuring light beam, with the vertex edge parallel to light slit 59, the two metal sides being welded together at an angle of 90. The two sides are provided at their base ends with welded fillet strips 55 which are tap ed to receive screws 56 securing the prism to the cell side wall, which at the same time serves as the prism base. The ends of the prism are sealed by triangular plates 57, which are secured to the prism sides by welding so that the prism is leak tight. Screws 5% secure the end plates to the side wall. A suitable gasket may be interposed between the prism and the cell wall to insure a leak tight seal at this point. Each of the prismsides is provided with a window 52 disposed at the same level as windows 52 hereinabove described and of the same design. The prism construction described has several important advantages, since it will be apparent that this design permits ready disassembly for purposes of cleaning orinspection and fillets 55. close oif the spaces along the base edges so that material cannot collect at these points and thereby change the composition of the standard material. The liquid standard solution is introduced into prism 8 through pipe coupling 58 and may be withdrawn through pipe cell chamber from a thermostatically controlled,

14: coupling 59 whenever a change in-standard is required. p The window glasses of both'cell 1 and prism 8 are strong, circular pieces of plane glass which are retained in place by annular rings 60 (refe'rf Figs. 12 and 13) which'are held in'place by three screws disposed jequidistantly around the pe-fl ripheries. The window plates are, inserted against the annular shoulder portions Bl, suitable resilient gaskets being' interposed on both sides of the glass to protect againstbreakage during assembly.

-As hereinbefore stated the refractive index characteristic of a material varies with tem-.

perature. Temperature control according to this inventionis achieved by maintaining both the cell construction above described,- The sample material is continuously circulated through the large capacity reservoir of the" type hereinbefore generally described. The standard material is preferably not circulated but is retained with-f in the confines of the hollow prism where its temperature is maintained at the same level asthat of the sample material.

The design of glass plate l4 shown in Figure 14 .is particularly suited to zero point adjust-- ment in the manner hereinbefore described.

The glass plate is supported by vertical shaft 62,:

angular displacement beingdetermined from calibration a by reading the rotation past base line 66 which is inscribed at the top of base 54.

, Drilled holes 6'! are provided in base 64 forthe reception of connecting screwsjoining plat [4 to base 32. When plate I4 is to be used to effect optical rebalancing it will bejunderstood .that

shaft 62 may be'provided with a gear wheeler.

other means (not shown) for driving connection w th the output shaft of motor 3|, andthe plate W111 then automatically assume such a position that the measuring light beam will be restored,

to its initial position along the edge of mirror H] for each separate value of differential refractive index. l

Phototubes l2 and I3, and electrometer tube l9,are enclosed in chamber 68 (refer Figs. 15 and 17), the front sid wall of which is provided with cut out light window 69. The rear wall of chamber 68 is slotted at 10 'to provide clearance for the travel of the mirrors supporting arm H which is integrally joined to advancing nut 72 threaded to micrometer screw H. Bracket members 73 provide bearing support for the un threaded ends of screw H which carriesfiintegral divided circle 14 for the direct measurement of mirror deflection, by means of call brations 74a and 14b thereon. Gear wheel15 attachedto screw l l is adapted tolengage with, a companion gear on the outputshaft of, mo-.

tor 3|. a l ,Photo'tubes fl and I3 are-mounted-upon th'e The lower end of shaft 62 is tapered cfiamiserwezns at-e ommen ievei and greasetained in place by clamps l6 and pillow blocks and rear upright strips 81! carryingspring' clips- Biaiell supported by'a base plate -8B which is drilled at eaxali' end to permit screw mounting.

upon shelf members T9? The plate holders sllpphi-t dcn'vefitionel grcund glass difiusin g' mates} wmc'n-"are utiliie'd to mssersethe light-reflected rromdividing mirror"; I 0 evemy over" the light sensxtlve 'ere'a o'f tlie pliototubes; thereby, to some" degree";- bii'lancingout'the effect ofany 'point in: equalities? i'rfp'hdtotube" element sensitivity;

iiig'ht snutteml '(rererFigs. 19' and'2'0) compfise's'a".vertic'i1 face plate provided witlr a cut ojllfli'glit" WifidiiWWfi-theopeningi afea of Which maybe adjusted by. means of light impenetrable pliite member 813+ which 'is supported f-rom top. shelf 89 Guide shaflsBOare-welded to the top corners of; plate-Wand slide freely through coinpanion holesimsh elf 89' .Plate 88 is supported" by.:- adjustinglwscrew ".91" connected therewith by' a slip ICGHETT-O'I "other J means permitting-Tree r6- tii'tionof the: screw with rsfibtto the plate. Screw fl' is threadedly sfijbj'orted bf'sh'elf 89; so tlibitthe eletatidfi'of the'iple temay' be varied by til ing itnuried iiead-"agpr screw 91" in one d1- rect ix'i" or the other. 'I'lie'botto'rir edge" of the face platei's tapbedat points" 93 to permit screw connectiori' with: shelves 1 92' v Light shutteiffafords 'a n'dvl means for ad-- Jiist'irig V the"sensitivities of the two phototubes-so that they 'are fsubstentially' equal.- phot'otubes will rarelyhav'e' the same inherent sensitivity andisincethe'reffctdmeter of this in wmonmngnpns by yir'tue' of balanced reflected light; it will beapparent that the light response ofthe"strongei-jhototiibe 'n'iiistbe reduced to'thelevel01""theweaker"phothtubeso that the responseso'ifboth'tubes will be equal wh'en-the di vijding o r refieets eii'u'al quentities of light tb 'e'ac'h fthetubesf Amofivement 'niethodfof' 'achievih'g'ithis initial sensitivity belancedstoeniployhfie'of the phototu es to be used determine mez'erdpoim pos'itioii' of'the" diyi'dingmirr'or s'aiiiiile" cell 1 and' fir-isi'n {I -both contain" only standard mate'- rial, under which conditions it will be understood thet the rneasu'r inglight beam" isnot defiectecl. Tneneaus of thesin'gle *ph'oto'tube 1 may be -connected" to a'-' sensitive galvanometer and readings taken" witli the phot'otubemountea'en' first-one side 0f thedividing mirror and then on the-other.- fI heposition=of the dividing mi'rror" may then be shi-ftem in onedirection or" the dtlief'im'til the phototuberesponse; as indicated" by the galvanometer reading, is exactly the same wlintlie bhotot'ube is mounted; on either sideof tli'eml'frdr'. The" other phototube to be used may th'efi'b'e mounted on the opposite side ofthe di alteringthejiositidn"oifthe'dividing mirror from iti l' b'aleiidsettifi'gf- The "strong'efphottfibe is masked by 'nioilifliiii'g shutter 8l' before" it and? turning down'screw 9i and its connected plate 88 Mi the; light responses oi are ex- A pairof instrument iS iIi-"COHIiltiOIi for use.

: edge so that precise division of the measuring light bea-m' may be effected;

Referring to Figure 16', the dividing mirror may be c'onvenie'ritly mounted. with anadhesive cei'n'ent' upon plate memb'er' 84 which'i's integrally; '1' joined to supporting" arm Tl The rear wall of ch'anlbe'rBB' isprovi'declwith slot 10 to'p'efl'ni't the passageof arm 'l'l therethrough, the mating stir-'- faces of the'slo't arid-thearm' being accurately machined so" that the slot surfaces serve as guiding-ways for" thehorizontal travel 01' the" located alor'ig" the" opposite edges; Advancing nu't T2' is preferably simlit so that its tensionagainst-- the* threa'd'smi screw Il may beadjusted bytightening serews '96 to compensate fol" wear" over long-'pei'iods of service:

In" practice; differential refractometers" can: structed' a'ccording to this" inventionhavepbs sessed a high sensitivity.

In one case the null-balancing embodiment was utilizedto' check theconcentration of rean01: water solution-in the range of 0 to 1.0 alcohol by volume; using pure water as the standard rrfate'rial in the hollow pri'si'n'i- A't 29.45 Cl, nH o=1.33200 while-fiia:i1:'1-.35662. A 1 by volume"alcohol-Water solution has a re-- fractive index value of 1.33242, the difference-in: refractive indexi An; from pure water my 1% alcohol" 'concentration'- being- 0100042, correspond-- ing to a-niovnlent of themirrors'dividing eage of 0.025 inch. The micrometer Screw utilized moved the mirror 0.0001 inch'for each' degree of rotation-of the'screw. In this' r'ange' the-relation between alcohol concentration and refractive in'dex' is nearly linear; so that a 0.1 alcohol solution had a reflective index value 014133204, corresponding to 'a movementof the niirr'ors dividing edge of 0-.0025irlchl- Using the helicalresistance"herei-nbefore described to actuate the; recordiii'g-v d'e'vic'e; A11"- values of the order" of 01000004; corresponding t'o 0-L0l% alcohol can: cent'z 'ationl could be detected with very close contrbl-ofth temperature of the sample and standa'zd materials. when the temperatures of the sdmiile and stenda'rd' materials are main tamedc'cnstsnt withi'ria range' 0130.1 0 alcohol coneentgation' changes of the order of about 0.03% by"voli1ffie*maybe detected; With' the reeo rdmg msteumem empldye'din tnesemeasu're means it wasne'cess'ar i to preset the range to withirif the lin'ii'ts' of' 0-to"4% alcohol concentritim-bwvomnie, corresponding to a' range of refractive index change of" 0 10013; but, it will be understood-'- thatfit ispossible to increase the range of indication substantially by increasing the scale span of i the recording instrument utilized by conventional methods known in the art.

In practice, a wide variety of sample cell designs may be utilized for the comparison of the selected standard material with the sample to be tested, the only common requirement in all cases being that one of the materials to'be compared must be interposed oblique to the measuring light beam. While it is generally preferred that the light enter the sample cell normally, in some casesit may be advantageous to utilize a design comprising a main hollow outer prism for containing the sample and a second smaller standard-containing prism mounted inside the first with its sides and base parallel to .the sides and base of the main prism. In this case it will be understood that the initial light deflection will be much greater than in the case where the light enters normally; however, the instrument will still comprise a differential refractometer within the meaning of the term as herein used. It ,will also be understood that the sample cell may simply comprise a two-part, light transparent container wherein the common wall separating the sample material iromthe standard materialis disposed obliquely across the light beam path. As a practical matter the oblique separationibetween sample and standard must be limited to an angle of, about 15 degrees to about 85 degrees with the path of the light arriving from the source to secure detectable deviationsof the measuring light in its traverse through the cell..

When a prism is used as a chamber for one of the components to be compared it is not necessary that the prism be of isosceles form. with both sidesof equallength, although the latter construction is generally preferred.

It will also be understood that the light emerging from the sample cell may be divided in other ways than by the dividing mirror construction whichhas been described. Thus, it is possibleto split the light into two portions by theuse of a light impenetrable plate disposed in a plane parallel to the line of light travel and then measure the quantities of light by direct impingement on phototubes located on each side of the plate. Or the splitting plate may be provided with reflecting surfaces operable to register the light on detecting phototubes located at otherpoints.

Where a dividing mirror is used to separate the emergent light, the micrometer screw may be housed within the chamber in which the phototubes and electrometer tube are mounted, and the extentof mirror movement indicated by a movable index scale supported upon guiding ways mounted within the slot in the rear wall, all in a manner well known in the art and therefore not further described herein.

It will be apparent that this invention is capable of variation and wide modification within its essential spirit, wherefore I intend to be limited only to the extent indicated by the scope of the following patent claims.

What is claimed is: I

1. A differential refractometer comprising the combination of a light source, a condensing lens, a restrictive light slit, a collimating lens, a light filter passing only light substantially continuous in intensity with wave length, a sample chamber disposed normal to the light path and provided with a space, for one of the liquid materials to be compared and with a hollow prism disposedwith its vertex parallel to the plane containing said restricting slit and its sides oblique to the light path for containing the second liquid material to be compared, a second condensing lens, a sharp-edged dividing mirror movably mounted in the plane of light deflection for splitting the once-refracted emergent light from said sample chamber into separate portions, and electrical means for measuring'the ratio of the amount of said once-refracted light in each of said portions, and for moving said dividing mirror to a new position where the separate light portions are equalized, thereby indicating the amount of deflection of said once-refracted light.

2. A diiierential rerractometer according to claim 1 wherein the means for measuring the ratio of light inthe separate portions comprises two phototubes connected in series-aiding relationship, a nrst powered circuit having a control element connected to a point between said phototubes, said first circuit passing current of a magnitude dependent upon the electrical potential of the point of connection or said control element between said phototubes, a second powered circuit connected in parallel relationship to said first powered circuit passing current independent of potential variations of the point of connection of said control element between said phototubes, means for ampliiying and transposing the net output of said powered circuits to an electrical signal of a phase determined by the electrical potential existing between said phototubes, and means responsive to said electrical signal for moving said dividing mirror to a new position where the light portions are equalized and for giving an indication of the amount of deflection of said once-refracted light.

3. A differential refractometer comprising the combination of a light source, a condensinglens, a restrictive light slit, ,acollimating lens, a light filter passing only light substantially continuous in intensity with wave length, a sample cham' ber disposed normal to the light path and provided with a space for one of they liquid materials to be compared and with a hollow prism disposed with itsvertex parallel to the plane containing said restrictive slit and its sides oblique to the light path for containing the second liquid material to be compared, a second condensing lens, a sharp-edged dividing mirror movably mounted in the plane of light deflection for splitting the once-refracted emergent light from said sample chamber into separate portions, separate phototubes mounted to receive said light portions, and means responsive to the degree and kind of electrical unbalance between said phototubes to move said dividing mirror to a new position where the separate light portions are equalized, thereby indicating the amount of deflection of said once-refracted light. v

4. A differential refractometer comprising in combination, a light source,-a condensing lens, a restrictive light slit, a collimating, lens, a light filter passing only light substantially continuous in intensity with'wave length, a sample chamber disposed normal to the light path and provided,

with a space for one of the liquid materials to be compared and with a hollow prism disposed with its vertex parallel to the plane containing said restrictive slit and its sides oblique to the light path for containing the second liquid material to be compared, a second condensing lens,

a, pair of phototubes connected in series-aiding relationship, a sharp-edged dividing mirror movably mounted in the plane of light deflectionior' splitting the once-refracted emergent light from said sample chamber into separate portions and for-reflecting each of said portions to one of the Mir of phototubes of substantially equal light Sensitivity, a first powered circuit having a control element connected to a point between said phototubes, said first circuit passing current of ama-g'nitude dependent upon the electrical potential'of the point of-connection of said control eleiiieht between said phototubes, a second powered circuit connected in parallel relationship to said first powered'circuit passing current independent of-potential variations of the point of connection of said control element between said phototubes, an electrical signal of a phase determined by the electrical potential existing between said phototubes, means for amplifying and t'ransp'osing the net output of said powered circuits to said ='electrical signal, and means responsive to said electrical sig'nal ro'r movingsaid dividing mirror to a new position where the light portions are equalized and'for giving an indication of the deflection or said light beam co'nv'e'rtible to difference in refractive index.

5. In a device for transforming changes of refr-active index of afluid into electricalindications or said changes-including means for producin'g a light beam, which comprises in combination, -a light source, aslit for constricting the-light toa broad line, a colliinating-lens through which the light beam passed, -a--filter traversing the light beam to render it substantially continuous I in intensity with wave length, a cell through which the light is passed andhavin'g-a window perpendicular to the direction of light travel to eliminate deflectionof the light beam tom-its course, separate phototubes and means for measuring the amount of refraction comprisin a dividing mirror having asharp-edge to s'plitth'e light-beam and *deflec't separate portions of it to each-of said tubes,-'a-lens and ag-lass plate through'which the light beam is passed to bring it into focus approximately at the plane defined by the sharp edge of'said mirror and the axes of the phototubes to deflec't the light to-said ph'ototubes, and means for 'determini ng 'the ratio of light intensities in the -two *split portions-ofthe light beamby measuring the ratios of responses or said phototubes to thereby indicate the amourit of light reiraction. h

6. In a device for' tr'ansfor mi'ng bha'n'ge's -of'retractive index of -a fluid into eleetri'cal indications of said chang'es --inolud-ing meah's for producing a light beam, which com rises in combination, a light source, a slit for constricting the light *to a broad line, a collimatin'g lens through which the light beam is p'assed,-a--fllter traversing the light beam -to render it substantiallyeontinuous in mtensity with wave length, a -cell throu"gh which the light is passed and having a window-perpendicular to the direction -of-li-ght-travel "to eliminate deflection of the light beam from its 'course, separate phototubes and means '"for -meas'uring the amount "of refraction comprising a dividing mirror havinga sharp edge tosplit thelightbeam and deflec't sep'ar'ate -p'ortion's of it to'each'ofsaid tubes, a lens and means --compri'sing 'a rotatable, plane parall'el, transparent plate interposed across the light path before T the dividing mirror to deflect the light a predetermined amount by passage 'thereth'r'oug'h to initially center "the refraoted'e'mergent lightat thezero point of equal light 5 reflection.

7. --In a difie'rential 'r efractometer, means 'for producin a refrac'ted light beam whichds substantially continuous in intensity with wave length, which comprise in combinatiomannt body of liquid to be compared, a second body of liquid to be compared disposed contiguous to-said first body, a restricting slit for said light beam, means for passing the light through saidlslit and thence normally through the first body aoI liquid and obliquely through-said second bodyof liquid. a, dividing mirror having a sharp leading edge for splitting the light beam by focusing therefracted emergent light upon saidleadin'g edge, a ipa'irrcf separate phototubes ofisubstantially equalzlight sensitivity and means for reflecting separate ,portions of 'saidlight to each of said tubes, actuating auxiliary means responsive to the ratio or the portions of said light reflected to each c! we phototube to move the dividing mirror toamew position to equalize the lightportions reflectedlby said mirronand indicate the amount 'oflight deflection by measuring the amount of mirror movement.

8. In a. differential refractometer including means for producing a retracted light beam Bubstantially continuous in intensity with wave length, which comprises in combination, a' light source, a slit for constricting thelight to abroad line, a refraction cell-and a focusing lens through which the light is passed and'having 'a window perpendicular to the direction of light travel 42 eliminate deflection of the light beam tram its course, a dividing mirror having a sharp edge 1m splitting the light beam byfocusing the emergent light of said beam upon said sharp edge, m'em for measuring the ratio of intensities in splitporti'onscomprising, two separately mounted phototubes of substantially "equal light sensitivity, said dividing mirror reflecting separate portions :ar saidrefractedlight from thefaces of saidmirror to each of saidseparate phototubes, 'a movable, plane-parallel transparent plate interposed across the path of said light beam between'the focusing means and said dividing mirror, actuatin auxiliary means responsive to the electrical unbalance between said phototubes to rotate said transparent plate to anew position to equalize the light-portionsreflected by saidmirrorgand means measuring the amount or plate movement to create an indication ottheli'ght deflection.

9. 'In adifferential refractometer, the 'combina-' tion comprising a light source, a restricting slit, afocusing lens, alight filter passing only light substantially continuous in intensity with wave length, a sample chamber disposed normalto-the light path and provided with a space ior li'quid sample material and -a second contiguous space for standard materia1,--said spaces'beingseparated along a line oblique to the light path-and disposed at-an angle of between about 15 degrees and about degreestherefrom,a sharp edgedmirror for dividing the refracted emergent light from said sample chamber-into separate portions, and means for measuring the ratio of the amount of said light in-each of said portions to therebyde termine the degreeof lightdeflectioncomprising a tilt' plate in combinationwith phototubesponnected in series-aiding relationship, 6a "first powered circuit having a control elen'ientconnected to-a point between said'phototubes, said first circuit passing current ofa magnitude dependent upon the electrical potential of thepoint of connection of said control element "between said phototubes, a second powered c'ircuit eonnected in parallel relationship to said flrst powered circuit passing 'current independent or potential "variations of the -point "or connection of said control element between said phototubes, and means responsive to the difference in the electrical outputs of said two powered circuits to register the degree of deflection of said refracted light.

10. A difierential refractometer comprising the combination of a light source, a vertically disposed light restricting slit, a focusing lens, a lightfilter passing only light substantially continuous in intensity with wave length, a sample chamber disposed normal to the light path and provided with a space for one of the liquid materials to be compared and with a hollow prism disposed with its vertex parallel to the vertical edges of said restricting slit and its sides oblique to the light ath for containing the second liquid material to be compared, means for dividing the refracted emergent light from said sample chamber into separate portions, comprising a sharp-edged mirror having a pair of inclined reflecting faces. and means for measuring the ratio of the amount v 22 of light in each of said portions to thereby determine the degree of deflection of said refracted light.

LEO G. GLASSER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,905,251 Styer Apr. 25, 1933 2,114,867 Wilson Apr. 19, 1938 2,136,682 Gilbert Nov. 15, 1938 2,139,474 Shepard Dec. 6, 1938 2,385,503 Glasser Sept. 25, 1945 2,413,208 Barnes Dec. 24, 1946 2,427,996 Seaman Sept. 23, 1947 2,445,044 Stamm et al July 13, 1948 2,483,102 Pierson Sept. 27, 1949 

